Many types of catheters have been developed for treating problems and diseases of body systems including the vascular, pulmonary, lymphatic, urinary, and other body systems that include one or more body lumens. Such catheters advantageously provide treatment by generally non-invasive techniques by permitting manipulation of distal features of such catheters from their proximal ends. These catheters may be made up of many components with properties selectively chosen for specific functions. And as a result, it is generally desirable to combine different components to obtain particular control aspects of such catheters. Generally, polymeric materials are used for such catheters because of medical use conditions and sanitation requirements and the like.
In particular, balloon catheters are frequently used to treat intravascular diseases by generally non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) and may include techniques for delivering medical devices such as stents and the like. These therapeutic angioplasty catheterization techniques are well known in the art and typically involve the use of a balloon catheter with a guide wire. A typical balloon catheter has an elongate shaft with an inner lumen and has a dilatation balloon attached proximate the distal end and a manifold attached proximate the proximal end. Typically these catheters are designed to be introduced into a body lumen over the guide wire which is slidably received within the inner lumen of the catheter. In use, the balloon catheter is advanced over the guide wire such that the dilatation balloon is positioned adjacent a restriction in a diseased vessel. Then, fluid under pressure is supplied to the balloon through the catheter lumen, expanding the balloon and opening the restriction in the vessel.
For stent delivery, systems have been developed utilizing catheters as part of the stent delivery system. In some applications, balloon catheters may be used to deliver stents where a stent can be delivered to a desired treatment site as a collapsed structure provided about a balloon. At the site, the balloon can be expanded to set the stent in place. Other stents, such as self-expanding stents, may also be delivered by catheter systems. In such a system, a catheter may be used to deliver a self-expanding stent to a treatment site, wherein the stent may be constrained by an outer sheath. Once the stent is properly positioned by manipulating the catheter, the outer sheath can be pulled away, such as by pulling a wire connected to the outer sheath, thereby allowing the self-expanding stent to expand and set in place.
In order to achieve a combination of desired properties at different parts of the catheters themselves, catheters have been developed by combining a plurality of tubing components together to define a catheter lumen. That is, a portion of the overall length of a catheter lumen may comprise a different tubing type component than another. These one or more portions may comprise tubing components of different physical characteristics and/or different materials. For example, a tip portion may be provided that is more resilient than the remainder of the catheter lumen for better crossability and to provide a softer leading end of the catheter for abutting body internal membranes and the like. Different materials include different polymeric materials from one another, for example, or similar polymers of different densities, fillers, crosslinking or other characteristics. In particular, a portion of a catheter lumen may comprise a material chosen for flexibility to follow a body lumen's path while another portion may comprise a material chosen for axial and/or torque transmission.
Balloons for use with these catheters are frequently prepared from a variety of polymeric materials depending on their intended use. Generally, these materials are required to possess elastomeric properties such that the dilatation balloon has the requisite compliance. That is, the balloon has a predetermined relationship between balloon diameter and dilatation pressure. Moreover, such balloons must be able to resist bursting at the relatively high pressures commonly employed during these procedures. Because some catheter component materials typically may not possess elastomeric properties for a particular application, the balloons can be prepared from a polymeric material which is different from, and is not readily bonded to, the material employed to fabricate the catheter.
In one well-known approach for joining dilatation balloons to catheters, resistance heated copper jaws are utilized to press the respective balloon shafts onto and against the catheter while the fusion takes place. A problem though is that the balloon and catheter may be deformed by the direct application of heat. Such application of heat can deform the balloon and catheter material and form small, random channels at the balloon to catheter interface. These channels are known to contribute to variations in the strength of different bonds and may cause generally poorly bonded balloons. To compensate for this variance, bonds are usually given a sufficient length to provide the requisite strength. Directly applied heat also may cause crystallization and stiffening of the balloon and catheter material, not only at the bond site, but also in both directions axially of the bond. Disadvantages that may arise from crystallization and stiffening at and around the bond include impeded trackability and crossability as well as reduced maneuverability.
Other approaches to bonding avoid the use of copper jaws, for example, U.S. Pat. No. 4,251,305 to Becker et al., the entire disclosure of which is incorporated herein by reference. Becker discloses a non-contact method for heat sealing a balloon onto a catheter. A length of thin tubing is slid over an elongated shaft of the catheter. Shrink tubing is installed over the thin walled tubing at its ends, and overlapping the shaft, and partially shrunk. Then, lamps provide further radiant energy to form gradually tapering thermoplastic joints that bond the tubing and shaft. The device employed for bonding utilizes three lamps that emit energy along the visible and infrared spectra. Each lamp is situated near an elliptical reflector, at one of the loci of the ellipse. The bond or treatment area is near the other focus. This approach avoids the problems arising from mechanical squeezing from the copper jaws, but some axial conductive heat transfer can still occur, which may be undersirable.
Another technique for bonding dilatation balloons and catheters involves directing laser energy along a fusion bond site. One such laser process is disclosed in U.S. Pat. No. 5,501,759 to Forman, the entire disclosure of which is incorporated herein by reference. In one embodiment, the invention of Forman may be used to weld an annular interface of a catheter and dilatation balloon. In this embodiment, a beam of laser energy is directed substantially at the annular interface. Then, the beam can be moved in an annular path along the interface, relative to the catheter and the dilatation balloon. This is accomplished by mounting the catheter and dilatation balloon concentrically on an axis, and rotating the catheter and dilatation balloon about the axis while maintaining the beam stationary. As an alternative, the catheter and dilatation balloon can be maintained stationary while optomechanical means can be used to rotate the beam.
Such laser welding techniques for raising the temperature of polymeric materials typically utilize a predetermined static laser power over a short pulse or multiple pulses. As such, the temperature of the polymeric material rises from the beginning of the weld pulse to the end of the weld pulse in a generally linear manner. This can cause the properties of the bonded region to vary undesirably. Moreover, variations in the material contact and seam condition for individual balloon catheters may further lead to variations in the properties of the bonded region.